1. Field of the Invention
The present invention relates to a device for cleaning and sterilizing the inside of a chamber, comprising a supply of sterilizing liquid for this chamber, and means for inducing, within this sterilizing liquid, variations in pressure, amplitude and frequency, and in the gradient of said variations, said means being adapted to generate cavitation within this liquid.
2. Description of Related Art
It has been observed that cavitation, in addition to its familiar undesirable effects in hydraulic systems, such as attack of surfaces, noise, and loss of contact with the liquid, has other characteristics which may prove beneficial in some applications.
The first of these characteristics is mechanical and makes it possible to go beyond the limits of capillarity in a cavitation regime. This property may therefore be of use when treating regions which are otherwise inaccessible.
The destructive properties can be used judiciously by exploiting the thermal wave which, although temporary, is nevertheless substantial. The same is true of the accompanying oxidation reaction. This is because the exothermal implosion of the vapor bubbles created by negative pressure on a microorganism releases its energy in a very short time and on a very small surface area, determining temporarily a very high temperature.
It is therefore the conjunction of mechanical, thermal and even chemical effects which makes it possible at one and the same time to improve the use of a cleaning and/or sterilizing agent and to increase its efficacy. The dissolution of one substance in another is thereby greatly enhanced and permits sterilization of a cavity or of a body immersed in a cavitation regime, which it would not be possible to obtain by simple rinsing or prolonged immersion with the same liquid agent.
As cavitation appears when know thermodynamic conditions in a defined liquid are satisfied, it suffices for the inside of a chamber which is closed and filled with liquid to be subjected to pressure variations which are adequate in their amplitude and form to generate cavitation in this liquid at its particular temperature. The effect of cavitation may be exerted on the liquid itself, on the walls of the container or on any body immersed therein.
The demands of the pressure signal are however very particular and are difficult to obtain solely by mechanical selection of the desired pressure levels and frequency.
The use of cavitation for cleaning and sterilizing has already been the subject of many applications in the medical field, or for cleaning and sterilizing medical or paramedical equipment. The combination of ultrasonic frequencies and of cavitation has also been proposed for cleaning and sterilizing. Reference may be made, by way of example, to DE 39 03 648 which relates to a method for inactivating viruses in a liquid by means of the cavitation generated by varying the flow speeds within the liquid. This method is implemented with the aid of a high-pressure pump and a homogenization valve placed downstream.
In EP 0,078,614, contact lenses are cleaned and disinfected in a saline solution in which cavitation is created at an ultrasonic frequency.
Another method for cleaning and sterilizing which combines ultrasound and cavitation is described in EP 0,595,783 and in U.S. Pat. No. 4,193,818. Cavitation combined with ultrasound has the disadvantage of attacking the cleaned surface.
It has also been proposed, in EP 0,299,919, to use cavitation for devitalizing teeth, an endpiece being fitted in a leaktight manner onto an opening formed to give access to the pulp chamber of the tooth. This endpiece comprises a liquid injector connected to a feed pump and a discharge conduit connected to a suction pump. The suction pump creates bubbles in the liquid, which the pressure pump causes to implode, thereby producing cavitation.
An improvement to the above device has been proposed in EP 0,521,119 in which a water-jet pump is arranged in the adjustable endpiece which can be fitted in a leaktight manner on the orifice of the pulp chamber of the tooth filled with Javel water. The inlet of this water-jet pump is connected to the outlet conduit of a piston pump, its outlet is connected to a discharge conduit, and its suction conduit opens into the pulp chamber. At each cycle of the pump, a reciprocating motion of a certain volume of liquid is produced in the discharge conduit due to the alternating compression and suction, in a conduit connecting the pump to the discharge conduit by way of a water-jet pump, generating alternating negative pressures and overpressures in the liquid of the pulp chamber, thus generating cavitation.
The first of these devices for devitalization requires two pumps and involves a high level of consumption of liquid, consisting of the treatment liquid itself. The second of these devitalization devices uses a single-action piston pump which is as it were the motor driving the water-jet pump, generating variations in pressure in the pulp chamber. The piston pump used for this purpose produces a sinusoidal pressure which, starting from the closure of a single-action valve, increases until it reaches the gradient of the sinusoid. Only the gradient is useful in creating cavitation, and this gradient must be as steep as possible in order to create a variation which is as sudden as possible. Given that the sinusoidal variation does not suffice by itself to cause the desired cavitation, it acts on the pressure of the pulp chamber by way of a body of liquid which it causes to move and works as a resonator to create the required sudden pressure variations by way of the water-jet pump.
It is an object of the present invention to attain required sudden pressure variations, but directly without the aid of a water-jet pump, that is to say without a positive pressure generator. To this end, the subject of the present invention is a device for cleaning and sterilizing the inside of a chamber. By using a switching member it is possible for a column of liquid, connecting this switching member to the sterilization chamber, to be brought into communication with two defined pressure levels, the difference between these corresponding to the desired amplitude, so that the gradient of the variation is very considerable, and only the losses of head in the conduits influence this gradient since the pressures of the two levels are constant. In addition, the pressure of just one of the two pressure levels must be created artificially, while that of the other level, corresponding to the highest pressure, is simply the atmospheric pressure. The system therefore functions as a spring piston which tends constantly to be brought back to one of its two positions by the return spring. In the case of the present invention, the spring is formed by the atmospheric pressure.